Employee Benefit Plans (Components of Net Periodic Benefit Cost Included in General and Administrative Expenses) (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2019	Dec. 31, 2018	Dec. 31, 2017
Pension Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	$ 291	$ 314	$ 284
Interest cost	489	448	476
Expected return on plan assets	(816)	(817)	(781)
Amortization of prior service cost	(4)	(4)	(3)
Amortization of actuarial (gain) loss, net	217	213	191
Settlements	59	8	13
Special termination benefits	26	1	4
Net periodic (benefit) cost	262	163	184
Other Postretirement Benefits
Defined Benefit Plan Disclosure [Line Items]
Service cost	22	23	20
Interest cost	78	70	82
Expected return on plan assets	(95)	(108)	(102)
Amortization of prior service cost	4	1	0
Amortization of actuarial (gain) loss, net	24	17	36
Settlements	0	0	0
Special termination benefits	1	0	0
Net periodic (benefit) cost	$ 34	$ 3	$ 36